4 Architecture model and concepts

23.2143GPPArchitecture enhancements for control and user plane separation of EPC nodesRelease 17TS

4.1 General concepts

The architecture and functionality for control and user plane separation of SGW, PGW and TDF is based on the following concepts:

– Interworking with networks not applying control and user plane separation is possible (i.e. in case of roaming scenarios);

– Split network entities can interwork with network entities that are not split within the same network;

– Split network entities have no requirement to update UE, and Radio Access Network;

– The SGW/PGW selection function of the MME/ePDG/TWAN described in TS 23.401 [2] and TS 23.402 [4] is used for the selection of the respective CP function;

– The configuration based mechanism (in PGW or PCRF) described in TS 23.203 [3] is used for the selection of the CP function of the TDF;

– A CP function can interface with one or more UP functions (e.g. to enable independent scalability of CP functions and UP functions).

4.2 Architecture reference model

4.2.1 Non-roaming and roaming architectures

This clause defines the complementary aspects of the architecture reference models specified in clause 4.2 of TS 23.401 [2] and clauses 4.2.2 and 4.2.3 of TS 23.402 [4] for GTP-based interfaces when SGW, PGW and TDF control and user planes are separated.

For S2a, S2b, S5 and S8 reference points, this architecture reference model is only supported with GTP-based interfaces. PMIP-based interfaces and S2c interface are not supported.

Figure 4.2.1-1 shows the architecture reference model in the case of separation between control plane and user plane. This architecture reference model covers non-roaming as well as home routed and local breakout roaming scenarios.

Figure 4.2.1-1: Architecture reference model with separation of user plane and control plane for non-roaming and roaming scenarios

NOTE 1: The -C or -U suffix appended to S2a, S2b, S5 and S8 existing reference points only indicate the control plane and user plane components of those interfaces.

NOTE 2: The architecture in figure 4.2.1-1 only depicts the case when the CP and UP functions of all SGW, PGW and TDF nodes are split. However, the other cases when the CP and UP function of only one of these nodes is split while the CP and UP function of the other interfacing node is not split, e.g. PGW’s control plane and user plane is split while SGW’s control plane and user plane is not split, are also supported. The split architecture of a node does not put any architectural requirements on the peer nodes with which it interfaces.

NOTE 3: TDF is an optional functional entity.

NOTE 4: Additional interfaces/reference points are documented in TS 23.401 [2], TS 23.402 [4], TS 23.060 [5] and TS 23.203 [3].

NOTE 5: For a roaming architecture with local breakout, the Gx interface is defined between the PGW-C and PCRF in the visited network.

NOTE 6: S11-U is the interface between MME and SGW-U, supporting CP CIoT EPS Optimisation (see TS 23.401 [2]).

4.2.2 Combined SGW/PGW architecture

The usage of a combined SGW/PGW documented in TS 23.401 [2] remains possible in a deployment with separated control and user planes. This is enabled by supporting an Sx interface with a common parameter structure for non-combined and combined cases. Figure 4.2.2-1 shows the architecture reference model for a combined SGW/PGW in the case of separation between control plane and user plane.

Figure 4.2.2-1: Architecture reference model with separation of user plane and control plane for a combined SGW/PGW

NOTE 1: The combined Sxa/Sxb shown in figure 4.2.2-1 only covers the functionality of Sxa and Sxb.

NOTE 2: S11-U is the interface between MME and combined SGW/PGW-U, supporting CP CIoT EPS Optimisation (see TS 23.401 [2]).

4.2.3 Reference points

This clause defines the complementary reference points of the architecture reference models specified in clause 4.2 of TS 23.401 [2] and clauses 4.2.2 and 4.2.3 of TS 23.402 [4] for GTP-based interfaces when SGW, PGW and TDF control and user planes are separated.

The reference points added to the reference points defined in TS 23.401 [2], TS 23.402 [4] and TS 23.203 [3] are the following ones:

Sxa: Reference point between SGW-C and SGW-U.

Sxb: Reference point between PGW-C and PGW-U.

Sxc: Reference point between TDF-C and TDF-U.

4.3 High level functions

4.3.1 General

This clause documents the existing functionality of SGW, PGW and TDF as described in TS 23.401 [2], TS 23.402 [4] and TS 23.203 [3].

Table 4.3.1-1: Existing functionality of SGW, PGW and TDF

Main functionality	Sub-functionality	SGW	PGW	TDF
A. Session management	1. Resource management for bearer resources	X	X
(default & dedicated bearer	2. IP address and TEID assignment for GTP-U	X	X
establishment,	3. Packet forwarding	X	X
bearer modification, bearer deactivation)	4. Transport level packet marking	X	X
	1. IP address allocation from local pool		X
	2. DHCPv4 / DHCPv6 client		X
B. UE IP address	3. DHCPv4 / DHCPv6 server		X
management	4. Router advertisement, router solicitation, neighbour advertisement, neighbour solicitation (as in RFC 4861)		X
	1. Forwarding of "end marker" (as long as user plane to source eNB exists)	X
C. Support for UE mobility	2. Sending of "end marker" after switching the path to target node	X	X
	3. Forwarding of buffered packet	X
	4. Change of target GTP-U endpoint within 3GPP accesses	X	X
	5. Change of target GTP-U endpoint between 3GPP and non-3GPP access		X
	1. ECM-IDLE mode DL packet buffering; Triggering of Downlink Data Notification message generation per bearer (multiple, if DL packet received on higher ARP than previous DDN); Inclusion of DSCP of packet in DDN message for Paging Policy Differentiation	X
D. S1-Release / Buffering / Downlink Data Notification	2. Delay Downlink Data Notification Request (if terminating side replies to uplink data after UE service request before SGW gets updated)	X
	3. Extended buffering of downlink data when the UE is in a power saving state and not reachable (high latency communication); dropping of downlink data (if MME has requested SGW to throttle downlink low priority traffic and if the downlink data packet is received on such a bearer (see clause 4.3.7.4.1a).	X
	4. PGW pause of charging procedure based on operator policy/configuration the SGW (failed paging, abnormal radio link release, number/fraction of packets/bytes dropped at SGW)	X	X
	1. UL/DL APN-AMBR enforcement		X	X
E. Bearer/APN policing	2. UL/DL bearer MBR enforcement (for GBR bearer)		X
	3. UL/DL bearer MBR enforcement (for nonGBR bearer on Gn/Gp interface)		X
	1. Service detection (DPI, IP-5-tuple)		X	X
	2. Bearer binding (bearer QoS & TFT)		X
	3. UL bearer binding verification and mapping of DL traffic to bearers		X
	4. UL and DL service level gating		X	X
	5. UL and DL service level MBR enforcement		X	X
	6. UL and DL service level charging (online & offline, per charging key)		X	X
	7. Usage monitoring		X	X
F. PCC related functions	8. Event reporting (including application detection)		X	X
	9. Request for forwarding of event reporting			X
	10. Redirection		X	X
	11. FMSS handling		X	X
	12. PCC support for NBIFOM		X
	13. DL DSCP marking for application indication			X
	14. Predefined PCC/ADC rules activation and deactivation		X	X
	15. PCC support for SDCI		X	X
G. NBIFOM	Non-PCC aspects of NBIFOM	X	X
H. Inter-operator	1. Accounting per UE and bearer	X	X
accounting (counting of volume and time)	2. Interfacing OFCS through reference points specified in TS 32.240 [9]	X	X	X
I. Load/overload control functions	Exchange of load/overload control information and actions during peer node overload	X	X
J. Lawful interception	Interfacing LI functions through reference points specified in TS 33.107 [10] and performing LI functionality	X	X
K. Packet screening function			X
L. Restoration and recovery		X	X	X
M. RADIUS / Diameter on SGi			X
N. OAM interfaces		X	X	X
O. GTP bearer and path management	Generation of echo request, handling of echo response, echo request timeout and Error Indication message	X	X

4.3.2 Functional split of SGW, PGW and TDF

4.3.2.1 Functional split of SGW

The following table describes the functionality of the SGW-C and the SGW-U.

All functionality performed by the SGW-U is controlled from the SGW-C and thus even if it is marked below as a SGW-U functionality only, there will be corresponding control functionality in the SGW-C.

NOTE: Functionality not marked for SGW-U is either only provided by SGW-C or does not require any specific SGW-U behaviour.

For interfaces not listed in the table below, Figure 4.2.1-1 describes whether they are terminated in SGW- C or SGW-U.

Table 4.3.2-1: Functional split of SGW

Main functionality	Sub-functionality	SGW-C	SGW-U	Comments
A. Session management	1. Resource management for bearer resources	X	X	See clause 5.10
(default & dedicated bearer	2. IP address and TEID assignment for GTP-U	X	X	See clause 5.4
establishment,	3. Packet forwarding		X
bearer modification, bearer deactivation	4. Transport level packet marking		X
	1. Forwarding of "end marker" (as long as user plane to source eNB exists)		X
C. Support for UE mobility	2. Sending of "end marker" after switching the path to target node	X	X	See clause 5.8
	3. Forwarding of buffered packet	X	X	See clause 5.9
	4. Change of target GTP-U endpoint within 3GPP accesses	X
	5. Change of target GTP-U endpoint between 3GPP and non-3GPP access			N/A
	1. ECM-IDLE mode DL packet buffering; Triggering of Downlink Data Notification message generation per bearer (multiple, if DL packet received on higher ARP than previous DDN); Inclusion of DSCP of packet in DDN message for Paging Policy Differentiation	X	X	See clause 5.9
D. S1-Release / Buffering / Downlink Data Notification	2. Delay Downlink Data Notification Request (if terminating side replies to uplink data after UE service request before SGW gets updated)	X
	3. Extended buffering of downlink data when the UE is in a power saving state and not reachable (high latency communication); dropping of downlink data (if MME has requested SGW to throttle downlink low priority traffic and if the downlink data packet is received on such a bearer (see clause 4.3.7.4.1a).	X	X	See clause 5.9
	4. PGW pause of charging procedure based on operator policy/configuration the SGW (failed paging, abnormal radio link release, number/fraction of packets/bytes dropped at SGW)	X		See clause 5.3.4
G. NBIFOM	Non-PCC aspects of NBIFOM	X
H. Inter-operator	1. Accounting per UE and bearer		X	See clause 5.3
accounting (counting of volume and time)	2. Interfacing OFCS through reference points specified in TS 32.240 [9]	X		See clause 5.3
I. Load/overload control functions	Exchange of load/overload control information and actions during peer node overload			As defined in CT WG4 TS 29.244 [12]
J. Lawful interception	Interfacing LI functions through reference points specified in TS 33.107 [10] and performing LI functionality	X	X	As defined in SA WG3-LI TS 33.107 [10]
L. Restoration and recovery				As defined in CT WG4 TS 29.244 [12]
N. OAM interfaces				As defined in SA WG5 TS 28.708 [13]
O. GTP bearer and path management	Generation of echo request, handling of echo response, echo request timeout and Error Indication message			As defined in CT WG4 TS 29.244 [12]

4.3.2.2 Functional split of PGW

The following table describes the functionality of the PGW-C and the PGW-U.

All functionality performed by the PGW-U is controlled from the PGW-C and thus even if it is marked below as a PGW-U functionality only there will be corresponding control functionality in the PGW-C.

NOTE: Functionality not marked for PGW-U is either only provided by PGW-C or does not require any specific PGW-U behaviour.

For interfaces not listed in the table below, Figure 4.2.1-1 describes whether they are terminated in the PGW-C or the PGW-U.

Table 4.3.2-2: Functional split of PGW

Main functionality	Sub-functionality	PGW-C	PGW-U	Comments
A. Session management	1. Resource management for bearer resources	X	X	See clause 5.10
(default & dedicated bearer	2. IP address and TEID assignment for GTP-U	X	X	See clause 5.4
establishment,	3. Packet forwarding		X
bearer modification, bearer deactivation)	4. Transport level packet marking		X
	1. IP address allocation from local pool	X		See clause 5.5
B. UE IP address management	2. DHCPv4 / DHCPv6 client	X		See clause 5.5
	3. DHCPv4 / DHCPv6 server	X		See clause 5.5
	4. Router advertisement, router solicitation, neighbour advertisement, neighbour solicitation (as in RFC 4861)	X		See clause 5.5
	1. Forwarding of "end marker" (as long as user plane to source eNB exists)			N/A
C. Support for UE mobility	2. Sending of "end marker" after switching the path to target node	X	X	See clause 5.8
	3. Forwarding of buffered packet			N/A
	4. Change of target GTP-U endpoint within 3GPP accesses	X
	5. Change of target GTP-U endpoint between 3GPP and non-3GPP access	X
	1. ECM-IDLE mode DL packet buffering; Triggering of Downlink Data Notification message generation per bearer (multiple, if DL packet received on higher ARP than previous DDN); Inclusion of DSCP of packet in DDN message for Paging Policy Differentiation			N/A
D. S1-Release / Buffering / Downlink Data Notification	2. Delay Downlink Data Notification Request (if terminating side replies to uplink data after UE service request before SGW gets updated)			N/A
	3. Extended buffering of downlink data when the UE is in a power saving state and not reachable (high latency communication); dropping of downlink data (if MME has requested SGW to throttle downlink low priority traffic and if the downlink data packet is received on such a bearer (see 4.3.7.4.1a).			N/A
	4. PGW pause of charging procedure based on operator policy/configuration the SGW (failed paging, abnormal radio link release, number/fraction of packets/bytes dropped at SGW)	X		See clause 5.3.4
	1. UL/DL APN-AMBR enforcement		X
E. Bearer/APN policing	2. UL/DL bearer MBR enforcement (for GBR bearer)		X
	3. UL/DL bearer MBR enforcement (for nonGBR bearer on Gn/Gp interface)		X
	1. Service detection (DPI, IP-5-tuple)		X
	2. Bearer binding (bearer QoS & TFT)	X
	3. UL bearer binding verification and mapping of DL traffic to bearers		X	See clause 5.2
	4. UL and DL service level gating		X
	5. UL and DL service level MBR enforcement		X
	6. UL and DL service level charging (online & offline, per charging key)	X	X	See clause 5.3
	7. Usage monitoring	X	X	See clause 5.3
F. PCC related functions	8. Event reporting (including application detection)	X	X	Note: User-plane related events such as application detection reporting supported in UP function, while control-plane related events such as RAT change etc. supported only in CP function.
	9. Request for forwarding of event reporting			N/A
	10. Redirection	X	X	See clause 5.11.3
	11. FMSS handling		X
	12. PCC support for NBIFOM	X
	13. DL DSCP marking for application indication			N/A
	14. Predefined PCC/ADC rules activation and deactivation	X	X	See clause 5.11.1
	15. PCC support for SDCI	X	X	See clause 5.11.4
G. NBIFOM	Non-PCC aspects of NBIFOM	X
H. Inter-operator	1. Accounting per UE and bearer		X	See clause 5.3
accounting (counting of volume and time)	2. Interfacing OFCS through reference points specified in TS 32.240 [9]	X		See clause 5.3
I. Load/overload control functions	Exchange of load/overload control information and actions during peer node overload			As defined in CT WG4 TS 29.244 [12]
J. Lawful interception	Interfacing LI functions through reference points specified in TS 33.107 [10] and performing LI functionality	X	X	As defined in SA WG3-LI TS 33.107 [10]
K. Packet screening function			X
L. Restoration and recovery				As defined in CT WG4 TS 29.244 [12]
M. RADIUS / Diameter on SGi		X	X	See clause 5.5
N. OAM interfaces				As defined in SA WG5 TS 28.708 [13]
O. GTP bearer and path management	Generation of echo request, handling of echo response, echo request timeout and Error Indication message			As defined in CT WG4 TS 29.244 [12]

4.3.2.3 Functional split of TDF

The following table describes the functionality of the TDF-C and the TDF-U.

All functionality performed by the TDF-U is controlled from the TDF-C and thus even if it is marked below as a TDF-U functionality only there will be corresponding control functionality in the TDF-C.

For interfaces not listed in the table below, Figure 4.2.1-1 describes whether they are terminated in the TDF-C or TDF-U.

Table 4.3.2-3: Functional split of TDF

Main functionality	Sub-functionality	TDF-C	TDF-U	Comments
E. Bearer/APN policing	1. UL/DL APN-AMBR enforcement		X	Not identical to APN-AMBR enforcement as it a) covers every flow in TDF session and b) does not cover other TDF sessions of the UE to the same APN
	2. UL/DL bearer MBR enforcement (for GBR bearer)			N/A
	3. UL/DL bearer MBR enforcement (for nonGBR bearer on Gn/Gp interface)			N/A
	1. Service detection (DPI, IP-5-tuple)		X
	2. Bearer binding (bearer QoS & TFT)			N/A
	3. UL bearer binding verification and mapping of DL traffic to bearers			N/A
	4. UL and DL service level gating		X
	5. UL and DL service level MBR enforcement		X
	6. UL and DL service level charging (online & offline, per charging key)	X	X	See clause 5.3
	7. Usage monitoring	X	X	See clause 5.3
F. PCC related functions	8. Event reporting (including application detection)	X	X	Note: User-plane related events such as application detection reporting supported in UP function, while control-plane related events such as RAT change etc. supported only in CP function.
	9. Request for forwarding of event reporting	X
	10. Redirection	X	X	See clause 5.11.3
	11. FMSS handling		X
	12. PCC support for NBIFOM			N/A
	13. DL DSCP marking for application indication		X
	14. Predefined PCC/ADC rules activation and deactivation	X	X	See clause 5.11.1
	15. PCC support for SDCI	X	X	See clause 5.11.4
H. Inter-operator	1. Accounting per UE and bearer			N/A
accounting (counting of volume and time)	2. Interfacing OFCS through reference points specified in TS 32.240 [9]	X		See clause 5.3
I. Load/overload control functions	Exchange of load/overload control information and actions during peer node overload			As defined in CT WG4 TS 29.244 [12]
L. Restoration and recovery				As defined in CT WG4 TS 29.244 [12]
N. OAM interfaces				Not defined by SA WG5

4.3.3 User Plane Function selection

The CP function of a functional entity performs selection of its respective UP function considering parameters such as UE’s location information, capability of the UP function and features required for an UE. Additionally, the selection of UP function shall consider UP function deployment scenarios such as centrally located UP function and distributed UP functions located close to or at the RAN site. The selection of UP function shall also allow deployment of UP functions with different capabilities, e.g. UP functions supporting no or a subset of optional functionalities.

For standalone CP functions:

– SGW’s CP function shall select SGW’s UP function;

– PGW’s CP function shall select PGW’s UP function;

– TDF’s CP function shall select TDF’s UP function.

Combined SGW/PGW’s CP function should select either combined SGW/PGW UP function or standalone SGW UP and PGW UP functions.

For details, refer to clause 5.12.

4.3.4 SGW-C Partitioning

If the SGW-U service area is smaller than the SGW-C service area, the SGW-C can be partitioned into multiple SGW-C partitions. Each of the SGW-C partition is aligned with the corresponding SGW-U service area. The MME treats the SGW-C partition as legacy SGW.

NOTE 1: There is only one Sxa reference point between one SGW-C and one SGW-U.

NOTE 2: This ensures that the TAI List allocated by the MME will only contain TAs that have connectivity to the SGW-U function serving the UE in case the MME uses the service area of the SGW-C partition when constructing the TAI List (and it cannot be assured that there is "full mesh" IP connectivity between the eNBs and the SGW-U function outside the SGW-U Service Area).

NOTE 3: If more than one SGW-U is selected to serve a given UE, these SGW-Us need to cover an area including at least the service area of the SGW-C.

4.4 Network elements

4.4.1 General

SGW-C and SGW-U jointly provide functionality equivalent to the functionality provided by SGW as defined by the TS 23.401 [2].

PGW-C and PGW-U jointly provide functionality equivalent to the functionality provided by PGW as defined by the TS 23.401 [2] and TS 23.402 [4], and the PCEF as defined by the TS 23.203 [3].

TDF-C and TDF-U jointly provide functionality equivalent to the functionality provided by TDF as defined by the TS 23.203 [3].

The clause 4.3.2 defines how the functional control and user plane split is done and which functionality SGW-C, SGW-U, PGW-C, PGW-U, TDF-C, TDF-U correspondingly support.

4.4.2 SGW control plane function

The SGW control plane function (SGW-C) provides the functionality of the SGW as defined by TS 23.401 [2] except for the functions that are performed by the SGW-U as described in table 4.3.2-1.

In addition, the SGW-C is responsible for selecting the SGW-U (as described in clause 4.3.3) and for controlling the SGW-U with respect to the functions described in table 4.3.2-1.

4.4.3 SGW user plane function

The SGW user plane function (SGW-U) provides the functionality described in this TS. The functions that are performed by the SGW-U are listed in table 4.3.2-1 together with a reference to a detailed functional description in clause 5 for some of them. The control parameters relevant for the SGW-U are described in clause 7.

NOTE: The standard allows certain functionalities to be supported in both SGW-C and SGW-U. For details refer to clause 5.

4.4.4 PGW control plane function

The PGW control plane function (PGW-C) provides the functionality of the PGW as defined by TS 23.401 [2] and TS 23.402 [4], and the PCEF as defined by the TS 23.203 [3] except for the functions that are performed by the PGW-U as described in table 4.3.2-2.

In addition, the PGW-C is responsible for selecting the PGW-U (as described in clause 4.3.3) and for controlling the PGW-U with respect to the functions described in table 4.3.2-2.

4.4.5 PGW user plane function

The PGW user plane function (PGW-U) provides the functionality described in this TS. The functions that are performed by the PGW-U are listed in table 4.3.2-2 together with a reference to a detailed functional description in clause 5 for some of them. The control parameters relevant for the PGW-U are described in clause 7.

NOTE: The standard allows certain functionalities to be supported in both PGW-C and PGW-U. For details refer to clause 5.

4.4.6 TDF control plane function

The TDF control plane function (TDF -C) provides the functionality of the TDF as defined by TS 23.203 [3] except for the functions that are performed by the TDF -U as described in table 4.3.2-3.

In addition, the TDF -C is responsible for selecting the TDF -U (as described in clause 4.3.3) and for controlling the TDF -U with respect to the functions described in table 4.3.2-3.

4.4.7 TDF user plane function

The TDF user plane function (TDF -U) provides the functionality described in this TS. The functions that are performed by the TDF -U are listed in table 4.3.2-3 together with a reference to a detailed functional description in clause 5 for some of them. The control parameters relevant for the TDF-U are described in clause 7.

NOTE: The standard allows certain functionalities to be supported in both TDF-C and TDF-U. For details refer to clause 5.